This invention relates to a photographic silver halide photosensitive material and more particularly, a photothermographic photosensitive material having high sensitivity and which has minimal sensitivity change with varying storage conditions.
Various types of photographic materials are used in the medical field. From the contemporary standpoints of environmental protection and space saving, it is strongly desired to reduce the quantity of spent solution. Needed in this regard is a technology relating to photothermographic photosensitive materials for use in medical diagnosis and general photography which can be effectively exposed by means of laser image setters and laser imagers and produce distinct black images having high resolution and sharpness. These photothermographic photosensitive materials offer to the customer a simple thermographic system which eliminates a need for solution type chemical agents and is not detrimental to the environment.
On the other hand, the recent rapid progress of semiconductor laser technology has made it possible to reduce the size of medical image output devices. As a matter of course, there were developed techniques relating to infrared-sensitive photothermal silver halide photographic material which can utilize a semiconductor laser as a light source. The spectral sensitization technique is disclosed, for example, in JP-B 10391/1991 and 52387/1994, JP-A 341432/1993, 194781/1994, and 301141/1994. The antihalation technique is disclosed, for example, in JP-A 13295/1995 and U.S. Pat. No. 5,380,635. Since the infrared exposure system permits the visible absorption of sensitizing dyes and antihalation dyes to be considerably reduced, a substantially colorless photosensitive material can be readily produced.
A combination of the thermographic technique with the infrared exposure technique allows for the production of a photosensitive material which eliminates a need for liquid.
Since spectral sensitizing dyes capable of absorbing infrared radiation, however, generally have a high reducing power due to a high HOMO (highest occupied molecular orbital), they tend to reduce silver ions in photosensitive materials to exacerbate the fog thereof. In particular, these photosensitive materials experience a substantial change of performance during storage under hot humid conditions and long-term storage. If dyes having a low HOMO are used for preventing deterioration of storage stability, spectral sensitization efficiency and sensitivity become low because their LUMO (lowest unoccupied molecular orbital) is relatively low. These problems relating to sensitivity, storage stability and performance variation arise not only with wet photographic photosensitive materials, but more outstandingly with photothermographic materials.
The supersensitization technique has been developed as one method for overcoming the problems associated with infrared sensitization. Known infrared supersensitizers for use in thermographic systems include aminopolycarboxylic acid derivatives as disclosed in JP-A 4241/1990, heterocyclic aromatic mercapto compounds and heterocyclic aromatic disulfide compounds as disclosed in JP-A 182639/1992 and 341432/1993. The aminopolycarboxylic acid derivatives have weak supersensitization and low sensitivity. The heterocyclic aromatic mercapto compounds and heterocyclic aromatic disulfide compounds suffer from the problem that sensitivity varies during storage under hot humid conditions.